The present invention relates generally to a cooling device including a vapor chamber for removing heat from a component connected with the cooling device. More specifically, the present invention relates to a cooling device including a heat mass with a plurality of fins and vanes and a vapor chamber that contains a phase change liquid at a low pressure that transforms to a vapor when heated to its boiling point by waste heat from the component so that the heat mass is cooled by the boiling of the phase change liquid and is convection cooled by an air flow through the vanes and fins.
It is well known in the electronics art to place a heat sink in contact with an electronic device so that waste heat generated by operation of the electronic device is thermally transferred to the heat sink thereby cooling the electronic device. With the advent of high clock speed electronic devices such as microprocessors (xcexcP), digital signal processors (DSP), and application specific integrated circuits (ASIC), the amount of waste heat generated by those electronic devices and the operating temperature of those electronic devices are directly proportional to clock speed. Therefore, higher clock speeds result in increased waste heat generation which in turn increases the operating temperature of the electronic device. However, efficient operation of the electronic device requires that waste heat be continuously and effectively removed.
Heat sink devices have become commonplace as a means for dissipating waste heat from electronic devices such as the types described above. In a typical application, a component to be cooled is carried by a connector that is mounted on a PC board. A heat sink is mounted on the component by attaching the heat sink to the connector using a clip or fasteners, for example. Alternatively, the heat sink is mounted to a PC board that carries the electronic device and fasteners or the like are used to connect the heat sink to the PC board via holes that are drilled in the PC board.
The need to drill holes can be one disadvantage to using fasteners because the fasteners or other mounting hardware used for connecting the heat sink to the PC board are usually electrically conductive and there is a risk of an electrical short due to contact between a PC board trace and the mounting hardware. Moreover, to avoid electrical shorts, the PC board traces can be routed around the hole, but that routing requires keep out zones that can complicate the routing of the traces.
Typically, a heat sink used in conjunction with a modem high clock speed electronic device will use an electrical fan mounted on top of the heat sink or within a cavity formed by cooling fins/vanes of the heat sink. The cooling fins increase the surface area of the heat sink and maximize heat transfer from the heat sink to ambient air that surrounds the heat sink. The fan causes air to circulate over and around the cooling fins thereby transferring heat from the cooling fins into the ambient air.
As mentioned previously, with continuing increases in clock speed, the amount of waste heat generated by electronic devices has also increased. Accordingly, to adequately cool those electronic devices, larger heat sinks and/or larger capacity fans (i.e. in CFM) are required. Increasing the size of the heat sink results in a greater thermal mass and a greater surface area from which the heat can be dissipated. Increases in fan capacity increase the air flow through the cooling fins.
There are disadvantages to increased fan and heat sink size. First, if the size of the heat sink is increased in a vertical direction (i.e. in a direction transverse to the PC board), then the heat sink is tall and may not fit within a vertical space in many applications, such as the chassis of a desktop computer. Second, if the PC board has a vertical orientation, then a heavy and tall heat sink can mechanically stress the PC board and/or the electronic device resulting in a device or PC board failure.
Third, a tall heat sink will require additional vertical clearance between the heat sink and a chassis the heat sink is contained in to allow for adequate air flow into or out of the fan. Fourth, if the heat sinks size is increased in a horizontal direction, then the amount of area available on the PC board for mounting other electronic devices is limited. Fifth, when the heat sink has a cylindrical shape formed by the fins it is often not possible to mount several such heat sinks in close proximity to each other because air flow into and out of the fins is blocked by adjacent heat sinks with a resulting decrease in cooling efficiency.
Finally, increases in fan size to increase cooling capacity often result in increased noise generation by the fan. In many applications such as the desktop computer or a portable computer, it is highly desirable to minimize noise generation. In portable applications that depend on a battery to supply power, the increased power drain of a larger capacity fan is not an acceptable solution for removing waste heat.
In the above mentioned heat sink with cooling fins there are additional disadvantages to mounting the fan within a cavity formed by the fins. First, a substantial portion of a heat mass of the heat sink is partially blocked by the fan because the fan is mounted directly on the heat mass and therefore blocks a potential path for heat dissipation from the heat mass because air from the fan does not circulate over the blocked portion of the heat mass.
Second, without the fan, a depth of the fins could extend all the way to a center of the heat mass; however, the depth and surface area of the fins is reduced by a diameter of the fan because the fan is mounted in a cavity having a diameter that is slightly larger than the fans diameter to provide clearance for the fan blades. Consequently, the heat mass of the heat sink must be made broader to compensate for the reduced surface area of the fins. The broader heat mass increases the size, cost, and weight of the heat sink.
Third, the reduced depth of the fins makes it easier for the fins to be bent if damaged. One possible consequence of a bent fin is that it will contact and damage the fan blades and/or cause the fan to stall thereby damaging the fan or causing the fan to fail. Fourth, because the fan is mounted in the cavity formed by the fins, power leads for the fan must be routed through a space between the fins. Sharp edges on the fins can cut the power leads or cause an electrical short. In either case, the result is that the fan will fail. Fifth, glue is typically used to mount the fan to the heat sink and the glue can get into the fan and cause the fan to fail. Any of the above mentioned fan failure modes can lead to a failure of the electronic device the heat sink was designed to cool because air circulation generated by the fan is essential to effectively dissipate waste heat from the electronic device.
Some prior heat sinks attempt to overcome the aforementioned disadvantages of a larger heat mass or increased fin area by using vapor chamber that is filled with a phase change liquid at a low pressure. Typically, the phase change liquid has a low boiling point so that it will boil and convert to a vapor phase in response to waste heat from a component that is thermally connected with the heat mass. The vapor chamber is press fitted into a body of the heat sink. In some instances, an outer casing of the vapor chamber is expanded to achieve a tighter contact between the vapor chamber and the heat sink. Typically, a metal joining process such as brazing or soldering is used to seal the vapor chamber.
One disadvantage of the prior heat sinks with a vapor chamber is that their performance (i.e. efficiency at dissipating waste heat) deteriorates considerably when the vapor chamber is made to tilt from a vertical axis thereby decreasing heat transfer to the phase change liquid.
Another disadvantage is that there are micro voids and/or larger gaps between the vapor chamber and the heat sink that result in an increase in a thermal resistance between the heat sink and the vapor chamber. Consequently, heat transfer from the vapor chamber to the heat sink is reduced.
Consequently, there is a need for a cooling device with a vapor chamber that allows the cooling device to be tilted from a vertical axis while still maintaining heat transfer to a phase change liquid. There is also a need for a cooling device with a vapor chamber that eliminates micro gaps between the vapor chamber and the cooling device so that there is a low thermal resistance between the vapor chamber and the cooling device.
In view of the foregoing, a brief summary of some of the exemplary embodiments of the present invention are presented in this summary. Some simplifications and omissions may be made in this summary, which is intended to highlight and introduce some aspects of the present invention, but not to limit the scope of the present invention in any way. Detailed descriptions of the preferred embodiments adequate to allow one of ordinary skill in the art to understand, make, and use the present invention are provided following this summary.
Broadly, the present invention is embodied in a cooling device for dissipating waste heat from a component to be cooled. The cooling device includes a heat mass with a base, a chamber bore extending inward of the base and a boss symmetrically positioned about an axis of the heat mass. The boss includes a land and a threaded bore extending through the boss to the chamber bore. A thermal core is connected with the base and includes a stepped face that extends into the chamber bore and a mounting surface adapted to thermally connect the thermal core and the heat mass with the component to be cooled. A plug including a step face and a threaded neck that extends from the step face. The threaded neck is threaded into the threaded bore of the boss. The plug also includes a plug cavity formed in the threaded neck and a plurality of plug fins that are spaced apart to define a plug slot between adjacent plug fins. A vapor chamber is defined by the plug cavity, the chamber bore, and the stepped face. A phase change liquid is sealed in the vapor chamber at a low pressure and the phase change liquid is in contact with a portion of the stepped face.
A plurality of vanes are connected with the heat mass and are spaced apart to define a primary slot between adjacent vanes that extend to the heat mass. The vanes have a surface area that increases in a radially outward direction from the axis of the heat mass and the vanes include at least one secondary slot extending through a portion of each vane to define a plurality of fins in each vane. The vanes include a top face, an aerodynamically profiled inner wall that includes a first portion extending from the boss and terminating at a second portion that extends to the top face of the vanes. The inner walls of the vanes define a chamber that surrounds the boss The vanes also include an outer wall that has a surface profile that widens from the base of the heat mass to the top face and includes therebetween a smooth curved portion, a draft portion, and a smooth radially outward portion.
Waste heat in the component is thermally conducted into the thermal core and the heat mass and is dissipated from the heat mass by an air flow through the chamber, the primary slots, the secondary slots, and the plug slots. Waste heat is also thermally conducted into the thermal core and is dissipated by causing the phase change liquid to boil and change from a liquid state to a vapor state. The vapor rises into the vapor chamber and contacts the plug cavity and the chamber bore where it cools upon contact and converts back to the liquid state.
One advantage of the cooling device of the present invention is that the stepped face of the thermal core allows the cooling device to be tilted from a vertical axis while still maintaining heat transfer to the phase change liquid so that the phase change liquid boils and is converted to the vapor phase thereby dissipation waste heat from the thermal core.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.